Uses in chemistry

This reaction has limited synthetic value but it is used in purification procedures. Contaminated aldehydes in a solution precipitate as the bisulfate adduct which can be isolated by filtration. The reverse reaction takes place in presence of a base such as sodium bicarbonate or sodium hydroxide and the bisulfite is liberated as sulfur dioxide.[2]

Uses in food

Sodium bisulfite is used in almost all commercial wines, to prevent oxidation and preserve flavor. In fruit canning, sodium bisulfite is used to prevent browning (caused by oxidation) and to kill microbes.[9]

In the case of wine making, Sodium bisulfite releases sulfur dioxide gas when added to water or products containing water. The sulfur dioxide kills yeasts, fungi, and bacteria in the grape juice before fermentation. When the sulfur dioxide levels have subsided (about 24 hours), fresh yeast is added for fermentation.

It is later added to bottled wine to prevent oxidation (which makes vinegar), and to protect the color of the wine from oxidation, which causes browning. The sulfur dioxide displaces oxygen in the bottle and dissolved in the wine. Oxidized wine can turn orange or brown, and taste like raisins or cough syrup.

Bisulfite DNA sequencing

Sodium bisulfite is used in the analysis of methylation status of cytosines in DNA.

In this technique, sodium bisulfite deaminates cytosine into uracil, but does not affect 5-methylcytosine, a methylated form of cytosine with a methyl group attached to carbon 5.

When the bisulfite-treated DNA is amplified via polymerase chain reaction, the uracil is amplified as thymine and the methylated cytosines are amplified as cytosine. DNA sequencing techniques are then used to read the sequence of the bisulfite-treated DNA. Those cytosines that are read as cytosines after sequencing represent methylated cytosines, while those that are read as thymines represent unmethylated cytosines in the genomic DNA.[10]